Can you simply write overlays as GOL files and load them from non-OSM URLs? Assuming you use the appropriate coordinate grid you won’t need POIs to layer the relevant data, and if you choose to annotate OSM’s POIs further, you can save those annotations as a personal GOL that you optionally share with others, and that also enables cross-referencing derivations if you use (unverified: trust isn’t the point, uniqueness is) signing key fingerprint as the GOL author GUID.